This research examines changes in lexical access and naming in young children near the end of their second year. During this time, children show an unprecedented increase in the rate and number of new words they produce. Concomitant to this increase is a transitory rise in perseverative naming errors. These errors involve the names of familiar objects that have been said correctly by the child on past occasion. The changing pattern of the errors provides a unique window onto the structure and processes of the lexicon as it emerges in the course of early word learning. The findings from this research will extend existing models of speech production by accounting for developments in the word retrieval operations of very young children just learning to talk. The principal goals of this research are: (1) To test predictions about the sensitivity of children to the occurrence of perseverative naming errors. I will induce children's naming errors experimentally through small perturbations in the language processing system. (2) To determine the effects of differential practice in comprehending and producing words on the frequency of the error. I will use a microgenetic design to manipulate children's experience hearing and saying individual words. (3) To provide evidence for the claim that the rise and fall of errors is unique to the developmental period of initial word learning. I will test the naming performance of children who have productive vocabularies that are considerably beyond the early spurt in lexical growth.